Programmable logic devices exist as a well-known type of integrated circuit (IC) that may be programmed by a user to perform specified logic functions. There are different types of programmable logic devices, such as programmable logic arrays (PLAs) and complex programmable logic devices (CPLDs). One type of programmable logic devices, called the field programmable gate array (FPGA), is very popular because of a superior combination of capacity, flexibility and cost. A FPGA typically includes an array of configurable logic blocks (CLBs) surrounded by a ring of programmable input/output blocks (IOBs). The CLBs and IOBs are interconnected by a programmable interconnect structure. The CLBs, IOBs, and interconnect structure are typically programmed by loading a stream of configuration data (bitstream) into internal configuration memory cells that define how the CLBs, IOBs, and interconnect structure are configured. The configuration bitstream may be read from an external memory (e.g., an external PROM). The collective states of the individual memory cells then determine the function of the FPGA.
Even though FPGAs are very flexible and can be used to implement many circuits, they have some performance limitations, such as longer signal delays and lower gate counts. These limitations hinder the use of FPGAs on some high speed communication applications. This is because high speed communication circuits are very complex and require fast real-time processing of information. For these applications, application specific integrated circuits (ASICs) are generally used.
Unfortunately, communication circuits implemented as ASICs have several disadvantages. One such disadvantage is the time-to-market risks associated with the relatively long cycle time necessary for the implementation of a new ASIC design. An additional disadvantage of using ASICs for communication circuits is that ASICs are “hardwired” and must be redesigned for any new application.
In view of the foregoing, it is advantageous and therefore desirable to have available a programmable logic device which is capable of implementing complex and high speed communication circuits.